The present invention relates generally to blood apheresis and, more specifically, to a method and apparatus for more efficient separation and collection of blood components, specifically, blood platelets.
Apheresis or hemapheresis generally refers to the separation of blood or blood components into further components or fractions such as red cells, white cells, platelets and plasma. In typical apheresis procedures, whole blood is collected from a donor or patient, anticoagulant is added to the whole blood, and the anticoagulated whole blood is then separated into two or more desired components or fractions.
The separated components may be collected from a healthy donor for later administration to a patient. This is sometimes referred to as "donor apheresis". One of the most common donor apheresis procedures is plateletpheresis or platelet apheresis. In plateletpheresis, platelets are collected from a healthy donor. The collected platelets are then administered to, for example, cancer patients whose ability to generate platelets from their own bone marrow has been impaired by chemotherapy.
Alternatively, the separated components may be removed as part of the treatment of a patient. This is sometimes referred to as "therapeutic apheresis". One such therapeutic apheresis procedure is plasmapheresis. In plasmapheresis, plasma carrying a disease or other undesired substances is removed from a patient and replaced with normal plasma or other replacement fluid. Other types of therapeutic apheresis procedures include removal of white blood cells or platelets from patients with excess amounts of those components.
Currently, there are several commercially available hemapheresis systems for separating blood or blood components into further components or fractions. One such system is the Autopheresis-C.RTM. system sold by Baxter Healthcare Corporation of Deerfield, Ill. The Autopheresis-C.RTM. system includes a microprocessor-controlled instrument and a disposable tubing set attached to the instrument. The disposable tubing set comprises two portions that are integrally connected to each other. The Autopheresis-C.RTM. system may be used for various donor or therapeutic apheresis procedures, including plateletpheresis.
Typically, the collection of platelets using the Autopheresis-C.RTM. system proceeds in two stages or phases, as disclosed in U.S. Pat. No. 4,851,126 entitled "Apparatus and Methods for Generating Platelet Concentrate" which is incorporated by reference herein. In the first stage of the two stage system, the instrument and one portion of the tubing set are used to collect platelet-containing plasma often called platelet-rich plasma (PRP). During the first stage, whole blood is withdrawn from a donor and combined with an anticoagulant solution. The anticoagulated whole blood is introduced into a separation chamber, where it is separated into red blood cells and PRP. The red cells are returned to the donor and the PRP is collected in a container. After a sufficient volume of PRP has been collected in the container, the instrument and tubing set are disconnected from the donor, who is then free to leave.
After the first stage is completed, the portion of the tubing set used during the first stage is disconnected from the instrument and is replaced with the portion of the disposable tubing set used for the second stage of the procedure. During the second stage, the PRP that was collected in the first stage is introduced into a separation chamber where platelets are separated from plasma to provide platelet-poor plasma (PPP) and platelet concentrate. The platelet concentrate is directed to a plastic container, while the PPP is collected in a separate collection bag.
Another automated system for separating blood or blood components into fractions or further components is the CS-3000.RTM. Cell Separator, also sold by Baxter Healthcare Corporation. The CS-3000.RTM. Separator also includes a microprocessor controlled instrument and a presterilized, disposable tubing set attached to the instrument.
In a CS-3000.RTM. platelet procedure, whole blood is withdrawn from a donor and is mixed with an anticoagulant solution. The anticoagulated whole blood is introduced into a separation chamber where it is centrifugally separated into packed red cells and PRP. As whole blood continues to enter the separation chamber, the separated red cells and PRP exit the chamber. The red cells are returned to the donor while the PRP enters a second separation/collection chamber, where the PRP is separated into platelet concentrate and platelet-poor plasma (PPP). The PPP is removed from this chamber and is returned to the donor, leaving only the platelet concentrate in the separation/collection chamber.
With the advent of chemotherapy as a method of cancer treatment, the demand for platelets collected from healthy donors has grown considerably. In order to meet this demand, hospitals and other platelet collection centers must rely on the good will of volunteer donors willing to take the time to donate platelets. Accordingly, efforts are made to make platelet collection procedures as quick and easy as possible with minimal inconvenience to the donor. For this reason, it is the desire of those in the field of blood apheresis to provide methods and apparatus capable of collecting the maximum number of platelets from a given donor in as short a time as possible, while also reducing the risk of any adverse donor reactions during the procedure.
Increasing the platelet yield from a given donor also has certain medical benefits. For example, a platelet dose collected from a single donor is more desirable than a platelet dose that has been pooled from several random donors, because it does not expose the patient or platelet recipient to the blood of several individuals. Administering platelets from a single donor also allows the patient to identify specific donors and reduces the risk of "alloimmunization", a condition in which a patient will no longer respond to platelet transfusions.
Shorter collection times are desirable because they are less of a burden on the donor. From an administrative standpoint, reducing the collection time also allows for more platelet collection procedures to be scheduled and performed.
In addition, because of laboratory testing that must be conducted on the collected platelets and schedules of donors and patients that must be coordinated, several days may pass between the platelet collection from the donor and the platelet transfusion into the patient. Accordingly, it is necessary that the viability of the collected platelet product be maintained for an extended period of time. In the case of platelets, it is preferred that the collected platelets be capable of long-term storage (i.e. at least five (5) days).
The viability of platelets during storage is a function of several variables such as pH of the concentrate, the availability of nutrients, oxygen transmission through the storage container, etc. as is well known in the field. Typically, the initial pH and the nutrients, such as dextrose, are provided by the anticoagulant added to the whole blood at the beginning of the procedure.
In addition to the nutrients, the anticoagulant typically contains citrate. Citrate aids in (a) preventing blood from clotting as it travels through the tubing, (b) preventing blood from clotting as it is separated and (c) preventing platelets from clumping during storage. Although citrate can be metabolized by humans, too much citrate can cause adverse reactions, with symptoms such as chills and tingling in the fingers and around the mouth. Of course, during typical blood apheresis procedures, a quantity of citrate is contained with the red cells when they are returned to the donor or patient. If too much anticoagulant is added to whole blood during the apheresis procedure, the donor or patient may experience the "citrate reaction" described above. For this reason, it is important to control and preferably reduce the amount of anticoagulant added to the whole blood during an apheresis procedure.
Recently, systems and methods have been developed whereby platelet yield can be improved while reducing the amount of anticoagulant administered to the donor. U.S. Pat. No. 5,135,667 to Schoendorfer (which is incorporated by reference herein), describes a method and apparatus for improving platelet yield by adding selected (and reduced) amounts of anticoagulant solution Acid-Citrate-Dextrose-A (ACD-A) at different times during a platelet collection procedure. Schoendorfer utilized a single anticoagulant container from which a selected (and reduced) amount of anticoagulant ACD-A was added to the whole blood during the first stage of a platelet procedure on the Autopheresis C.RTM. system described above. After a preselected amount of platelet-rich plasma had been collected during the first stage of the procedure, additional ACD-A was then added to the platelet-rich plasma to prevent the platelets from coagulating during the separation of the PRP into platelet concentrate and PPP, and also to provide a sufficient amount of anticoagulant and nutrients so that the platelet concentrate may be stored for at least 5 days.
Specifically, Schoendorfer disclosed that reducing the amount of anticoagulant ACD-A added to whole blood (during the first stage of the procedure) from the previously accepted standard of 8% ACD-A to 6% or less ACD-A (per total anticoagulated whole blood volume) significantly improved the platelet collection efficiency and the platelet yield. Adding less anticoagulant to the whole blood and, as a result, less citrate to the whole blood had the additional benefit of reducing the amount of citrate returned to the donor with the red cells, thereby reducing the possibility of citrate reactions in the donor or patient.
Schoendorfer attributed a portion of the increase in platelet yield to less fluid volume dilution due to less anticoagulant. However, Schoendorfer could not explain the other portion of the increase in platelet yield. Moreover, Schoendorfer did not report any effect on the collection time.